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The purpose of providing dummy coils in a generator is to provide mechanical balance for the rotor.

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From which material field coils of DC generator are made of?

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Field coils of DC generator are usually made of copper.

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A dummy strain gage is used in a quarter bridge strain gage circuit to :  (A) compensate for changes in temperature and lead wire resistance  (B) produce more output voltage from the bridge  (C) increase the sensitivity of the bridge  (D) compensate lead wire resistance only

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A dummy strain gage is used in a quarter bridge strain gage circuit to : compensate for changes in temperature and lead wire resistance 

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Answer :

In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.

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The purpose of providing dummy coils in dc machine armature is to  (1) reduce eddy currents (2) increase voltage induced (3) decrease armature resistance (4) provide mechanical balance for the motor

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In a A.C. series motor armature coils are usually connected to commutator through resistance.

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The two pressure coils of a single phase power factor meter have the same dimensions and the same number of turns.

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Armature reaction in a generator results in demagnetisation of leading pole tip and magnetisation of trailing pole tip.

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If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be?

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If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be zero.

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In a separately excited generator supplying rated load the armature reaction is always present.

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In a level compounded D.C. generator, full load terminal voltage is equal to no-load terminal voltage.

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In case of a flat compounded generator voltage remains constant irrespective of the load.

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In a D.C. generator in case the resistance of the field winding is increased, then output voltage will decrease.

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In a D.C. generator, the critical resistance refers to the resistance of field.

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The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be?

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The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be 580 V.

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In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when there is no load on|he generator.

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The e.m.f. generated in a D.C. generator is directly proportional to speed of armature.

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In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when number of poles is 2.

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In a D.C. generator the ripples in the direct e.m.f. generated are reduced by using carbon brushes of superior quality.

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Magnetic field in a D.C. generator is produced by electromagnets.

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The demagnetising component of armature reaction in a D.C. generator reduces generator e.m.f.

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If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be crossmagnetisation as well as demagnetising.

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In a D.C. generator, the iron losses mainly take place in armature rotor.

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The total losses in a well designed D.C. generator of 10 kW will be nearly 500 W.

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In over compounded generator, full load terminal voltage is more than no load terminal voltage.

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A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be about 2 V.

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A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave will be of 5 Hz.

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An exciter for a turbo generator is a shunt generator.

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A D.C. generator can be considered as rotating amplifier.

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A cumulatively compounded long shunt generator when operating as a motor would be differentially compounded long shunt.

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If a D.C. generator fails to build up the probable cause could not be field resistance less than the critical resistance.

Description :

A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly?

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A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly 240 V.

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The armature core of a D.C. generator is usually made of silicon steel.

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A separately excited generator as compared to a self-excited generator is amenable to better voltage control, more stable, has exciting current independent of load current.

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For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?

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Wave winding

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The condition for maximum efficiency for a D.C. generator is variable losses equal to constant losses.

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The critical resistance of the D.C. generator is the resistance of field.

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Flashing the field of D.C. generator means creating residual magnetism by a D.C. source.

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D.C. generator generally preferred for charging automobile batteries is long shunt compound generator.

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Welding generator will have lap winding.

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In D.C. generators on no-load, the air gap flux distribution in space is flat topped.

Description :

A 8-pole, DC generator has a simplex wave-wound armature containing 32 coils of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm. The induced armature voltage is  (A) 96 V (B) 192 V (C) 384 V (D) 768 V

Answer :

A 8-pole, DC generator has a simplex wave-wound armature containing 32 coils of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm. The induced armature voltage is 384 V

Description :

Explain the choice of size and number of generator units in a power plant. 

Answer :

Selection of Size and Number of Generating Units:  1. The size/rating and number of generating units in such way that they approximately match with the load curve/load duration curve as ... power plant is connected to grid system then generating unit of higher capacity can be installed.

Description :

The fall in speed of a dc generator due to increase in load can be corrected by  (1) cooling the armature.. (2) increasing the excitation. (3) reducing the load voltage. (4) increasing the input to the prime mover

Answer :

It   can  be  corrected  by  increasing  the  input  to  the  prime  mover.

Description :

The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is :  (A) 256 W (B) 320 W (C) 500 W (D) 625 W

Answer :

The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is : 625 W

Description :

In a synchronous generator if the excitation increased from a low value to normal value, with a fixed load  (A) The armature current increases and the power factor decreases  (B) The armature current decreases and the power factor also decreases  (C) The armature current decreases and the power factor increases but is lagging  (D) The armature current decreases and the power factor increases and is leading

Answer :

In a synchronous generator if the excitation increased from a low value to normal value, with a fixed load The armature current decreases and the power factor increases and is leading

Description :

In a DC generator the windings of interpoles are connected :  (A) in series with main field winding, to create a pole,of same polarity as the main pole ahead in the direction of rotation.  (B) in series with main field winding, to create a pole of opposite polarity as the main pole ahead in the direction of ... in the direction of rotation.  (D) in series with the armature winding, to create a pole of opposite polarity as the main pole ahead in the direction of rotation.

Answer :

In a DC generator the windings of interpoles are connected :  in series with the armature winding, to create a pole of same polarity as the main pole ahead in the direction of rotation. 

Description :

In a synchronous generator delivering lagging power factor load  (1) the excitation emf leads terminal voltage by the power angle (2) the excitation emf lags terminal voltage by the power angle (3) excitation emf leads the terminal voltage by the power factor angle (4) excitation emf lags the terminal voltage by the power factor angle

Answer :

In a synchronous generator delivering lagging power factor load the excitation emf leads terminal voltage by the power angle

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